Differentiating discharge tube



Aug. 3, 1948. M. CAWEIN DIFFERENTiATING DISCHARGE TUBE Filed July 31, 1944 FIG.

OUTPUT SIGNAL AAAAAAA NPUT SIGNAL INVENTOR MADISON CAWEIN TIME ATTORNEY Patented Aug. 3, 1948 DIFFERENTIATING DISCHARGE TUBE Madison Cawein, Fort Wayne, Ind., assignor, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application July 31, 1944, Serial No. 547,407

This invention relates to means for obtaining the derivative of an electric signal, and particularly to a novel differentiatingelectron discharge tube.

It is frequently desired to utilize differentiating means whereby an output signal is obtained which is representative of changes of an electric input signal. Devices of this type are used, for instance, for selecting or separating various types of synchronizing pulses which are required in the transmission of television pictures. Such difierentiating means are sometimes used in connection with an integrating means either for selecting diiferent types of electric pulses or for amplifying them.

To this end differentiating networks have gen erally been used heretofore. In one type of differentiating network a series condenser is employed in connection with a shunt resistor. Differentiation of an electric signal may alsobe obtained by inductive means such as by transformer coils. However, these .prior differentiating networks have the drawback that their frequency response isfairly limited, that is they will only respond to electric signals within a limited frequency range. Another drawback of prior differentiating means is that they can not amplify the input signal simultaneously with the differentiation thereof.

It is an object of the present invention, therefore, to provide a novel differentiating means which has a much wider frequency range than prior devices.

A further object of this invention is to provide a novel electron discharge tube for obtaining the derivative of an electric input signal.

In accordance with the present invention, there is provided an electron discharge tube for differentiating an input signal comprising an evacuated envelope having a collecting anode dis-. posed therein, and an electron gun for developing an electron [beam and directing it towards the collecting anode. The intensity of the electron beam is controlled in accordance with the input signal. An electrode is arranged to be responsive to changes in intensity of the electron beam. For

deriving an output signal representative ofchanges of the input signal, an output circuit is operatively connected to the electrode.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

' '7 Claims. (Cl. 250-2'7) In the accompanying drawing, Fig. 1 is a schematic representation of the electron discharge tube of the invention, while Fig. 2 is a set of curves illustrating input and output signal cur rents and referred to in explaining the operation of the invention.

Referring now more particularly to Fig. 1, there is provided an electron discharge tube l comprising an evacuated envelope 2 having a reentrant stem 3. Electron gun 4 has its leads connected through reentrant stem 3 and includes cathode 5, control element or control grid 6 and first anode I. Cathode 5 is connected to the negative pole of battery 8 through biasing resistor'lfl. The negative pole of battery 8 is grounded as shown in the drawing. Condenser H bypasses resistor H! to ground. First'anode'l is connected to the positive pole of battery 8, and hence is positive with respect to cathode 5. Second anode or collecting anode I 2 is disposed in envelope 2 opposite first anode 1. Collecting anode I2 is connected to battery 8 .as shown and may be kept at a slightly;

negative potential with respect to first anode 1. However, if desired anode l2 may also be kept at the same or even a higher positive potential than anode 1.

Control grid 6 is connected through condenser l3 with the input signal obtained from lead I l.

The input signal is impressed across grounded resistor 15 for developing voltage variations which lic coating on the inner wall of envelope 2. Elec trode 16 may be electrically connected to first anode 1, as shown and hence has the same potential as anode 1.. Although electrode l6 may be omitted if desired it is helpful in the operation of electron discharge tube I by keeping the inner wall of envelope 2 at a uniform reference potential which may be that of anode I or anode l2. A second electrode I! arranged in envelope 2 is spaced and electrically insulated from electrode l6. Preferably electrode I1 is ring-shaped as shown.

Electrode H is connected to an output circuit including amplifier 20. The output signal obtained from electrode 11 is impressed across grounded resistor 2| and utilized for controlling grid 22 of amplifier 20. Grid 22 is connected through resistor 2| to the negative pole of battery 23, grounded as shown. Cathode 25 of amplifier 20 is connected to ground. The positive pole of battery 23 is connected to anode 26 through resister 21'. The amplified output signal is impressed across resistorl'l and is obtained from lead 28. Magnetic coil 30 surrounds envelope 2. Coil 30 is connected to battery 3! for generating a transverse magnetic field.

The electron discharge tube of the invention operates inthe iollowingmanners By means of-electron gun l anelectron beam is developed in the customary manner and is directed towards second anode I2 which collectsthe electrons and returns theinto the electric circuit. Preferably, the potential between anodes l and I2 should be zero or even negative so that the electrons do not acquire a, high; velocity which would require a collecting anode-ofigreazt.

heat dissipating capacity. The thus developed electron beam may be focused-by magnetic coil 30. However, it may not be necessary toemploy a special focusing coll provided the electrons of heb amoo not-imnin eupon either e ectrode 69, lectrode l.

Th vin ut .s gnaloi which the derivative is t e. o tained. is onnected. to control g i 6. through condenser i3, Thesignal is impressed.

across grounded resistor 15, and. the thus obtained voltage variations serve for controlling the intensity of'the electron beam developed by electron gun 4: Hence, the intensity of the electron beam is at any, moment directly proportional to the instantaneous input signal ampli-. tude impressed across resistor l5;

Fig. 2 shows a set of curves which may be help-.

fuli for explaining the manner of. operationof the electron discharge, tube of the invention. In 2;the current has been plotted against time as indicated, and the lower curve represents the inputsignal or the electron beamcurrent, while theupper curve of Fig. ,Zrepresents the outputsignal current; As long as the electron beam current remains constant no chargeis induced in electrode ll. However, when the beam intensity changes from the horizontalcurve portion 33: to transient curve portion. a corresponding positive charge is induced in electrode 1-1: A change of the electron beam current corresponds to a change of the electron density. of

the beam. Accordingly, when a region of higher electron beam density approaches electrode I1,

the induced=positive charge increases until the regionof; higher beam density passes through electrode I'l whereupon the induced positive charge decreases again, as, shown in the upper curve 35 of Fig. 2'.- Hence, curve 35 isthederivati ve ofcurve portion 34; Again, when the,

beam intensity remains constant, as shown in curve portion 36; no charge is induced in electrode ll; When the intensity of'the electron beam current is reduced again, as shown in tran-' si'entcurve portion 31; a corresponding charge ofopposite sign is induced in electrode H, as represented by curve 38 of Fig. 2; Inthis manner-=current impulses are produced in the output;

are amplified-in amplifier-2n in the customary The output signal obtained through,

manner. lead 28-is thus representative of changes in in: tensityof the electron beam which in turn cor-,- responds tochanges of-the input signal;

Care-should -*be taken that electrodes l6 and 4 I l are arranged so that no electrons from the electron beam will reach them. As indicated in the drawing electrode I! should have a fairly small Width.

In view of the fact that variations of the input signal are utilized for controlling the intensity of an electron beamlit will-beperfectly obvious that, the electron discharge tube of the invention has practically no frequency limitations. The derivative of any input signal may be obtained where the frequency of the input signal lies within the radio frequency range including the high frequencies.

The: input signal only serves for controlling control grid 6.,- which in turn determines the intensity of the electron beam. Hence, it may be said that the electron discharge tube of the invention, also amplifies the output signal. For further amplifying the output signal a conventional amplifier 20 has been shown, but. it. is .to be understood that'the discharge tube of the in.- vention may be used without such a supplemental; amplifier arrangement.

While there has been described what is'.at present considered the preferred embodiment of the invention, it-willbe obvious to those skilled in the art that various-changesandmodiflcations may be made therein without departing. from the invention, audit is; therefore, aimedin the appended claims-to cover, all; such changes andmodifications as fall'within the true spirit' and scope of the invention.

What is claimed is 1.- An electron discharge tubefordifierentlat ing a transient input signal comprising an evacuatedenvelope, a collecting anode disposed. in said envelope, an electron gun for developing-an" electron beam and directing it towards said collecting anode, means operatively-connected-to said electron gun for controlling the-intensity of said electron beam in accordance withsald input signal, an electrode'of comparatively small width-arranged to have a charge induced there invin response to changes in intensity of said electron beam, and an output circuit operativelyconnected to-said electrode for deriving an output signalrepresentttiveof changes ofsaiddmputsignaL. 2. An electron discharge tube for difi erentlah ing-an aperiodic input signal comprising an evacuated envelope a collectin'g anoded-lsposedln said envelope, an electron gun including a control element for developing an electron beam and directing. it towards-said collecting anode, means-opveratively connected to said control element for controlling theintenslty-of said electron-beanr-ln accordance with said "input signal, anelectrode disposed adjacent the path ofsaid eleotron'beam" and capacitively coupled tosaid electron-beam to have a charge induced =therein= in response to changes inintensity of said electron beam, said electrode having awidth such that thetransittime of the electrons of said beam therethrough is comparatively short and an output circuit operatively connected -to-said electrode for deriving:

an output signal representative of changes of said."

input signal.

32 An electron-"discharge tube for difierentiating a, transient input signal comprising-an evacuated envelope, a collecting anodedisposed in said.

envelope, an electron gun including a control ele ment for developing, an electronbeam and directing it towards vsaid collecting anode, means operatively connected to said control element for controlling the intensity of said electron beam in ac cordance with said input signal, an electrode disposed adjacent to said electron beam and arranged so that electrons from said electron beam will not impinge upon it, saidelectrode being arranged to have a charge induced therein in response to changes in intensity of said electron beam and being nonresonant to said input signal, and an output circuit operatively connected to said electrode, said electrode having a small width so that the electrons of said electron beam will pass therethrough in a comparatively short time, thereby to derive an output signal representative of changes of said input signal.

4. An electron discharge tube for differentiating an input signal comprising an evacuated envelope, a collecting anode disposed in said envelope, an electron gun including a control element for developing an electron beam and directing it towards said collecting anode, a first electrode extending substantially between said electron gun and said collecting anode and disposed in such a manner that electrons from said beam will not impinge upon it, means for keeping said first electrode at a constant reference potential, means operatively connected to said control element for controlling the intensity of said electron beam in accordance with said input signal, a second electrode disposed parallel to the dire-ction of movement of said electron beam in such a manner that electrons from said beam will not impinge upon it and spaced and electrically insu lated from said first electrode, said second electrode having a comparatively small width and being arranged to have a charge induced therein in response to changes in intensity of said electron beam, and an output circuit operatively con-- nected to said second electrode for deriving an output signal representative of changes of said input signal.

5. An electron discharge tube for difi'erentiating an input signal comprising an evacuated envelope, :a collecting anode disposed in said envelope, an electron gun including a control element for developing an electron beam and directing it towards said collecting anode, means for focusing said electron beam, a first electrode extending substantially between said electron gun and said collecting anode and arranged as an inner coating of said envelope in such a manner that electrons from said beam will not impinge upon it, said first electrode being arranged to create a field free space between said electron gun and said collecting anode, means operatively connected to said control element for controlling the intensity of said electron beam in accordance w h. said in t signal, a second ring-shaped electrode disposed parallel to the direction of movement of said electron beam in said field free space in such a manner that electrons from said beam will not impinge upon it and spaced and electrically insulated from said first electrode, said second electrode having a comparatively small width and being arranged to have a charge induced therein in response to changes in intensity of said electron beam, and an output circuit operatively connected to said second electrode for deriving an output signal representative of changes of said input signal.

6. The method of differentiating a transient input signal in an electron discharge tube including an electrode, said method comprising developing an electron beam and directing it so that it does not strike said electrode, collecting the electrons of said beam, controlling the intensity of said beam in accordance with said input signal, limiting the transit time of said electrons through said electrode, inducing a charge in said electrode in response to changes in intensity of said beam, said charge being representative of the derivative of said input signal, and deriving an output signal from said electrode representative of said induced charge.

7. The method of differentiating a transient input signal in an electron discharge tube including an electrode, said method comprising developing and focusing an electron beam so that it does not strike said electrode, collecting the electrons of said beam, controlling the intensity of said beam in accordance with said input signal, limiting the transit time of said electrons through said electrode, inducing a charge in said electrode in response to changes in intensity of said electron beam, said charge being representative of the derivative of said input signal, and deriving an output signal from said electrode representative of said induced charge.

MADISON 'CAWEIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,220,839 Hahn Nov. 5, 1940 2,243,829 Brett et al June 3, 1941 2,276,320 Linder Mar. 17, 1942 2,284,751 Linder June 2, 1942 2,313,886 Nagy et a1 Mar. 16, 1943 2,363,962 Hell Nov. 28, 1944 2,376,707 McCoy "final--." May 22, 1945 

